In optical character recognition systems, video image information is reduced to a black/white decision from multi-level gray scale information before character recognition can be accomplished. The performance of any character recognition technique is dependent upon the quality of the video information being processed. The technique for reducing multi-level image information to black/white decisions determines, in part, the quality of the video image. One such technique for data reduction to black/white images is referred to as correlation. Correlation techniques include those described in U.S. Pat. Nos. 3,761,876 and 4,162,481.
In processing carbon, or carbonless, copies of an original document such as, for example, credit card receipt documents, many image scanning devices cannot produce a high quality image to capture all information on the document. Since the contrast of the carbon on the background is very low, standard thresholding techniques for image processing fail to produce an image of acceptable quality. Additional imaging problems occur due to noise, including smudges, stray matter and inherent non-uniform characteristics of the paper. Therefore, existing correlation techniques are inadequate for the processing of video images where print contrast ratios are low.
A need has thus arisen for a video processing system to enable optical character recognition devices to be able to read multi-level gray scale information from a variety of documents and forms and where such information is printed on non-white documents and/or documents having noisy backgrounds. Additionally, a need has arisen for a video processing system which will enable optical character recognition devices to read light characters that are typically not imaged correctly by standard image scanners.